The OGL is designed to allow companies to reuse elements of the various D&D systems in new RPG systems.

Here's a bit of a brain dump for you, just in point form (I'm not a lawyer, this is not legal advice, do your own research):

- You can't copyright the rules of games, only the artistic or literary expression of those rules (such as pictorial representation of tables and text descriptions).- You can't copyright or trademark rules or phrases (such as Hit Points, Ability scores, etc).- If you use the OGL, you can't refer to D&D by name.- The OGL lets you use D&D's spell list and monsters but you may have to use a WotC designated OGL versions of those things (check this yourself).- WotC has copyright on some specific monsters (Beholders, etc), which are outside of the OGL.- If you don't use the OGL, you can make a game system that is very similar like D&D, but needs different spell names and descriptions.- You don't have to pay royalties is you use the OGL.- The game system doesn't have to be free if you use the OGL (AFAIK)- You can use any dice and any mechanics you want, they are not copyrightable.- As long as you don't use the OGL, you can make a supplement for any game system without infringing their copyright.- As long as you don't use the OGL, you can state that your system is compatible with D&D.

I don't use the OGL for my system, Heroes Against Darkness. Much of the underlying game mechanics for my system are similar to 4th Edition, but I have my own magic system, so there is nothing in the system that infringes anything copyrightable that belongs to WotC.

Otsego, OK, I did do some research a while back, so there are some terms we have to clear up:OGL: This is a license to make and use terms, mechanics etc from D&D 3.5. The main requirement for OGL was that you needed a Players Handbook to make a character. If that were the case, you had a free license to use everything in the SRD if I recall. According to WOTC, this has been deprecated, although it can be argued that it still can be used for D&D 3.5. WOTC has made it very clear that the OGL did not and will not apply to D&D 4 and higherd20 System License: This was a more restrictive license than OGL. It was also for D&D 3.5. The key was, you were allowed to use certain logos, etc, but you had less leeway on the rules interpretations. This was also deprecated, but may still be applicable to D&D 3.5.

GSL: This is the license WOTC uses for D&D 4. It is much more restrictive in its license and the one thing that killed the aftermarket for D&D 4 is the clause that allows it to be revoked at any time without notice. By and large it allows you to use terms, etc. from the SRD and add definitions, but not redefine what they mean. You can exclude content from the SRD (e.g., there are no Dragonborn in my setting), but you cannot make Dragonborn 3 feet tall and unable to intimidate even smaller creatures.

I am not a lawyer, but my understanding is similar to Justin's. You cannot copyright game mechanics, but you can copyright game text. So, you can use the word Strength, but make sure your verbiage describing it is different from WOTC's (what words you use to describe what Strength means, not its final meaning).

Honeslty, I don't think anyone has challenged the ability to still use OGL on D&D 3..5 material that wasn't already doing it before D&D 4 came out. I am not sure the legal standing on that and the D&D 4 GSL license is pretty particular about what you can and can't do. Still, you might be able to use that to your advantage since we didn't get a d20 System License avalanche of product like we did in D&D 3.5.

I'm writing a book about procedurally generating adventures for the d20 system, and intend to use the d20 systems license because I will not be referencing anything in the player's handbook or monster manual, but would like to have the d20 on my cover.

- As long as you don't use the OGL, you can make a supplement for any game system without infringing their copyright.- As long as you don't use the OGL, you can state that your system is compatible with D&D.

That seems to contradict what I've heard elsewhere. Can you site a reference?

Copyright does not protect the idea for a game, its name or title, or the method or methods for playing it. Nor does copyright protect any idea, system, method, device, or trademark material involved in developing, merchandising, or playing a game. Once a game has been made public, nothing in the copyright law prevents others from developing another game based on similar principles.

Copyright law barely restricts copying games. It doesn't restrict compatible works, as long as you don't copy actual text (as opposed to terminology, which can't be copyrighted); I don't think I've ever seen a game supplement copy actual text from the game it was made for. I'm sure they exist, but they're rare.

For compatible works, two court cases to look at are Sega v. Accolade, in which Accolade made games for use with a Sega system without permission from Sega; and Lewis Galoob Toys, Inc. v. Nintendo of America, Inc. in which a compatible product was made for use with a Nintendo game system without permission of Nintendo.

As far as advertising compatibility, this is a statement of fact or not fact. If it's true, it's legal to say it. You can see more on the use of trademarks at http://cyber.law.harvard.edu/metaschool/fisher/domain/tm.htm and http://www.ftc.gov/bcp/policystmt/ad-compare.htm. If you look around, you'll see the use of trademarks for compatible use all over the place. Manufacturers make car parts and advertise that they are compatible with a specific make of car; they make parts for kitchen appliances and advertise that they are compatible with that particular brand of appliance, and so on. In general, in the United States, this sort of compatible-with advertising, like comparative advertising, is encouraged.